Question

\(A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+.....+\frac{1}{9900}\)

Answer 1

\(A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{9900}\)

\(A=\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+....+\frac{1}{99.100}\)

\(A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+....+\frac{1}{99}-\frac{1}{100}\)

\(A=\frac{1}{4}-\frac{1}{100}=\frac{6}{25}\)

Vậy A=6/25

Answer 2

\(A=\frac{1}{4\times5}+\frac{1}{5\times6}+\frac{1}{6\times7}+.....+\frac{1}{99\times100}\)

\(A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+.....+\frac{1}{99}-\frac{1}{100}\)

\(A=\frac{1}{4}-\frac{1}{100}\)

\(A=\frac{24}{100}=\frac{6}{25}\)

Answer 3

cảm ơn bạn nha!!!

Answer 4

A=1/20+1/30+1/42+...+1/09900

A=1/4.5+1/5.6+1/6.7+...+1/99.100

A=1/4-1/5+1/5-1/6+1/6+-1/7+.....+1/99-1/100

A=1/4-1/100=6/25